The book outlines the physical principles of operation and the basics of technical applications of solid-state oscillatory systems that use the effect of internal reflection of electromagnetic waves in dielectric bodies located in open space or in microwave transmission lines. The electrodynamic theory of the structures under consideration includes the analysis of lower types of oscillations and azimuth types of high-order oscillations, as well as mathematical modeling of resonant phenomena in waveguide-dielectric systems. The modern level of research on the properties of dielectric resonators is combined with the presentation of the basics of engineering implementation of resonant devices based on thermostable ceramic materials, the use of which leads to an improvement in the weight and size characteristics of radio electronic equipment in 50 : .. 100 times. For scientists in the field of radio engineering, radiophysics and electromics of the ultra-high frequency range.